An engine provides torque by combusting an air-fuel mixture in an engine cylinder. The combustion increases pressure and temperature within the cylinder to cause a piston within the cylinder to move. The moving piston applies a force to the engine crankshaft and causes it to rotate, thereby providing engine output torque. However, some portion of the cylinder gases may pass by the piston and enter the engine crankcase. The gases that enter the engine crankcase can be evacuated and reintroduced to the engine intake system so that engine hydrocarbon emissions may be reduced. In some engine systems, the crankcase gases flow from the crankcase to the engine intake via a positive crankcase ventilation (PCV) valve located along the PCV path. In some example systems, the PCV path starts at a valve cover and ends at the intake manifold. During engine operation, the PCV valve increases a restriction between the intake system and the crankcase during periods of higher intake manifold vacuum, and it reduces the restriction between the intake manifold and the crankcase during periods of lower intake manifold vacuum. In this way, the engine crankcase can be maintained at a slight vacuum so that hydrocarbons may be drawn from the engine crankcase to the engine intake system.
Although evacuating the engine crankcase of gases can reduce engine emissions, it also poses other issues. For example, under some conditions, it is possible to draw oil or oil mist through the PCV valve. In U.S. Pat. No. 4,515,137, a flow restriction is placed in the PCV path to limit the amount of oil drawn via vapor through the PCV path and into the engine. The oil precipitates out of the vapors when the vapors impinge on the restriction.
The above-mentioned method can also have several disadvantages. Specifically, the restriction in U.S. Pat. No. 4,515,137 can still allow oil to flow to the engine intake system if engine oil accumulates at PCV path inlet. In particular, the possibility of drawing oil from the engine crankcase and cylinder heads to the PCV path increases when the engine is exposed to lateral or centripetal force, and the restriction shown in U.S. Pat. No. 4,515,137 appears to offer little protection from oil egress related to lateral or centripetal force. Lateral or centripetal force may be experienced by an engine when a driver enters a curve or drives in a circle on a skid pad. The engine and vehicle tend to stay in a straight path, but the vehicle tires exert a force on the pavement that causes the vehicle and engine to turn. Likewise, the engine oil tends to stay on a straight path so it tends to accumulate at one side of the engine depending on the direction of lateral or centripetal force. In V configuration engines, the cylinder heads define the widest extent of the engine. As such, engine oil tends to accumulate in one of the engine cylinder heads during periods when the engine is exposed to lateral or centripetal forces. The engine oil that accumulates in the cylinder head as a result of lateral or centripetal acceleration can increase the possibility of passing oil through the PCV path in some systems since liquid oil may be driven into the PCV path.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine system for improving engine crankcase ventilation. One example of the present description includes an engine system, comprising: an engine; and a mechanically operated valve coupled to the engine, the valve limiting flow of from a crankcase of the engine to a PCV passage when a centripetal or a lateral force acting on the engine exceeds a threshold amount.
By closing a valve during times of higher lateral or centripetal force, it is possible to limit flow between an engine crankcase and intake system so that less oil is drawn into the engine intake system. In one example, a valve is comprised of a flapper that is coupled to a hinge. The hinge allows the flapper to respond to lateral and centripetal forces acting on the engine. For example, if a threshold amount of lateral force is exerted on an engine during a maneuver, the valve can close and limit the flow of vapors and liquid oil into the PCV path. Consequently, engine emissions and oil consumption may be reduced.
The present description may provide several advantages. In particular, the approach may reduce engine emissions that are related to a PCV system. Further, the present description may reduce system cost as expensive pumps may not be required to limit oil flow through the PCV system. Further still, the present description may provide simplified engine controls since the system in some examples may limit PCV path flow by a sole mechanically actuated device.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.